The purpose of this study is to investigate whether the offspring of patients with essential hypertension show a different renal vascular response to ace inhibitors with captopril than do the offspring of normotensives. It also involves defining the locus of ace inhibition responsible for the increase in renal blood flow. The specificity of the influence on renal blood flow is assessed by identifying the influence of the ace inhibitor on the renal vascular response to angiotensin II.